This invention is generally in the field of dewatering wet particulate matter, and more particularly to methods for increasing the rate of dewatering sludge, pulp fibers, or other solid particulate materials and for increasing the solids content of a dewatered cake.
Industrial processes can produce wet solids that require treatment before disposal, use, or reuse. Examples of such processes include the biological treatment of wastewater and the manufacture of pulp and paper. The wet solids are commonly referred to as sludge, and generally comprise a suspension of particles in a liquid. An example of treating sewage sludge is described in U.S. Pat. No. 6,808,636 to Ward et al., which is incorporated herein by reference.
Conventional techniques for treating wet solids include the steps of promoting flocculation of particles and then dewatering of the flocculated particles. Chemical thickeners, such as polymers and lime, are generally used to promote flocculation of the particles to form flocs. Dewatering techniques, which are well known in the art, are used to produce a cake for disposal. Non-limiting examples of such techniques include pressing and centrifugation of the flocculated particles. The resulting cake typically comprises between approximately 15 and 50% solids (i.e., about 85 to 50% water content).
Disposal methods for the cake typically include means such as landfilling, burning, or landspreading. The water content of the cake is merely a deadload. Accordingly, it would be highly advantageous to reduce the water content of the final cake as much as possible, which can be achieved by increasing the solids content of the cake. Thus, there is a need for a method to increase the solids content of a cake derived from dewatered wet solids.
Dewatering is also critical in other applications. For instance, dewatering is particularly important in the processing of fibers, such as pulp. See, for example, U.S. Pat. No. 6,103,064 to Asplund et al., which is incorporated herein by reference. In a conventional process, the pulp is thickened through drainage or pressing during various process operations, for example in a papermaking process. Improving the drainage rate or the solids content of the drained pulp would improve throughput and increase production. Accordingly, a need exists for a method to increase the rate of dewatering, in order to maximize the throughput of the dewatering device.